Gas discharge tube

ABSTRACT

In a gas discharge tube, a first discharge path-induction portion is arranged between a first discharge path-limit portion and a second discharge path-limit portion. A voltage is applied to the first discharge path-induction portion from the outside. As a result, an active starting discharge capable of passing through a first opening of the first discharge path-limit portion is produced between a cathode portion and the first discharge path-induction portion. As a consequence, there is facilitated the discharge at a starting time to pass through a second opening. As a consequence, there is achieved a rapid starting of discharge between the cathode portion and an anode portion. Therefore, in order to achieve further enhancement of brightness, there can be carried out with ease a further miniaturization pertaining to the openings, in terms of its area size, of the discharge path-limit portion while the starting properties being kept excellent, without any increase in a voltage at the starting time of the lamp so much.

TECHNICAL FIELD

The present invention relates to a gas discharge tube, and in particularto a gas discharge tube used as a light source for a spectroscope, achromatography or the like.

BACKGROUND ART

There is disclosed as a prior art pertaining to the related technicalfield a gas (deuterium) discharge tube in Japanese Patent Laid-OpenNo.6-310101 publication. In a gas (deuterium) discharge tube describedin this publication, there are arranged two metal partition walls withinthe discharge path between an anode and a cathode, wherein each of themetal partition walls is provided with small holes, whereby thedischarge path is caused to be narrowed. As a result, it is madepossible to obtain light with a high luminance by means of the smallholes on the discharge path. Further, provision of three or more metalpartition walls could lead to a further higher luminance. The smallerholes are made, the higher luminance of light there can be obtained.

DISCLOSURE OF THE INVENTION

On considering the above-described conventional art, the presentinventor has found the following problems to be solved. That is,although in the above-described conventional gas discharge tube, thesmall holes of each metal partition wall could be used for narrowing thedischarge path, so as to enhance luminance, there must be increased adischarge starting voltage to the greater extent, as the small holes aremade smaller, as also described in this publication, with the resultthat there is a marked restriction on the diameter of the small holes orthe number of metal partition walls.

The present invention has been made in order to solve theabove-described problem, and an object thereof is to provide a gasdischarge tube excellent in starting properties while achievingenhancement of luminance.

A gas discharge tube according to the present invention emits apredetermined light from a light emitting window of a sealed containerwith a charged gas toward the outside by producing a discharge between acathode portion and an anode portion enclosed in the container. The tubecomprises: a first discharge path-limit portion, arranged in a midway ofa discharge path between the anode portion and the cathode portion, andprovided with a first opening for narrowing the discharge path; a seconddischarge path-limit portion, arranged in a midway of the discharge pathbetween the first discharge path-limit portion and the anode portion,and provided with a second opening for narrowing the discharge path; anda first discharge path-induction portion, arranged between the firstdischarge path-limit portion and the second discharge path-limitportion, and electrically connected to an external power source.

In the gas discharge tube, in case where light with high luminance is tobe created, it is insufficient to simply make an opening portion fornarrowing the discharge path smaller. The smaller the opening portion ismade, the greater difficulty arises in causing discharge at a time oflamp starting. Therefore, in order to improve starting properties of alamp, there is need to generate a remarkably large potential differencebetween the cathode portion and the anode portion. As a result, it hasbeen confirmed in an experiment that the service life of the lamp isshortened. In view of the foregoing, in a gas discharge tube of thepresent invention, a first discharge path-induction portion is arrangedbetween a first discharge path-limit portion and a second dischargepath-limit portion. A voltage is applied to the first dischargepath-induction portion from the outside in order to improve the startingproperties of the lamp even if the discharge path has been narrowed. Asa result, a starting discharge capable of passing through a firstopening of the first discharge path-limit portion is produced between acathode portion and the first discharge path-induction portion. As aconsequence, it is facilitated for the discharge at a starting time topass through a second opening. As a consequence, there is achieved arapid starting of discharge between the cathode portion and an anodeportion. Therefore, in order to accomplish further enhancement ofbrightness, there can be carried out with ease a further miniaturizationpertaining to the opening, in terms of its area size, of the dischargepath-limit portion while the starting properties being kept excellent,without any increase in a voltage at the starting time of the lamp somuch.

Further, it is preferable that the first discharge path-limit portionand the second discharge path-limit portion are electrically insulatedfrom each other. By adopting such a constitution, the first dischargepath-limit portion and the second discharge path-limit portion can beset to different potentials, so that the starting properties of the lampcan be improved.

Furthermore, it is preferable that a distal end portion of the firstdischarge path-induction portion is conical. By adopting such aconstitution, the density of charged particles can be made higher at adistal end of the first discharge path-induction portion so that thestarting properties of the lamp is made further better.

Furthermore, it is preferable that the first and second openings of thefirst and second discharge path-limit portions are formed at bottomportions of cup portions spread towards the light-emitting window. Byadopting such a constitution, arc balls are securely created at the cupportions of the first and second discharge path-limit portions so that afurther enhancement of luminance can be achieved by creation of the twoarc balls.

Moreover, it is preferable that the gas discharge tube further comprisesa third discharge path-limit portion, arranged in a midway of thedischarge path between the second discharge path-limit portion and theanode portion, and provided with a third opening for narrowing thedischarge path. This serves to produce light with high luminance to acertain extent.

Further, it is preferable that the second discharge path-limit portionand the third discharge path-limit portion are electrically insulatedfrom each other. The second discharge path-limit portion and the thirddischarge path-limit portion can be set to different potentials so thatthe starting properties of the lamp can be improved even in case ofusing three discharge path-limit portions.

In addition, it is preferable that the third opening of the thirddischarge path-limit portion is formed at a bottom portion of a cupportion spread towards the light emitting widow. When such aconstitution is employed, an arc ball is securely produced at the capportion of the third discharge path-limit portion so that a furtherenhancement of luminance can be achieved.

Furthermore, it is preferable that the gas discharge tube comprises asecond discharge path-induction portion, arranged between the seconddischarge path-limit portion and the third discharge path-limit portion,and electrically connected to an external power source. By employing thesecond discharge path-induction portion, the starting properties of thelamp when utilizing three discharge path-limit portions are furtherimproved.

Further, it is preferable that a distal end portion of the seconddischarge path-induction portion is conical. When such a constitution isemployed, a density of charged particles can be made higher at thedistal end of the second discharge path-induction portion, so that thestarting properties of the lamp is further made better.

Furthermore, it is preferable that the second discharge path-inductionportion is applied to a voltage higher than that applied to the firstdischarge path-induction portion. Thereby, the starting discharge can begenerated smoothly.

A gas discharge tube according to the present invention emits apredetermined light from a light emitting window of a sealed containerwith a charged gas toward the outside by producing a discharge between acathode portion and an anode portion enclosed in the container. The tubecomprising: a first discharge path-limit portion, arranged in a midwayof a discharge path between the anode portion and the cathode portion,and provided with a first opening for narrowing the discharge path; anda second discharge path-limit portion, arranged in a midway of thedischarge path between the first discharge path-limit portion and theanode portion, and provided with a second opening for narrowing thedischarge path. The first discharge path-limit portion and the seconddischarge path-limit portion being electrically insulated from eachother.

In the gas discharge tube, the first discharge path-limit portion andthe second discharge path-limit portion are electrically insulated fromeach other in order to make a starting properties of a lamp excellenteven if the discharge path is narrowed. Thereby, the first dischargepath-limit portion and the second discharge path-limit portion can beset to different potentials. Therefore, by adjusting each potential,discharge at a starting time is facilitated to pass through the insideof the second opening. As a result, discharge between the cathodeportion and the anode portion is started rapidly. Therefore, in order toachieve a further enhancement of luminance, there can be accomplishedwith ease a further miniaturization, of the opening, in terms of itsarea size, in the discharge path-limit portion while the startingproperties being kept excellent without any increase in the voltage atthe time of lamp starting so much.

Further, it is preferable that the second discharge path-limit portionis shielded from the cathode portion by an insulating material. Withsuch a constitution, there is prevented occurrence of an abnormaldischarge due to bending around-discharge extending from the cathodeportion toward the second discharge path-limit portion.

Furthermore, it is preferable that an annular spacer of insulatingmaterial for positioning the second discharge path-limit portion and theanode portion is provided between the second discharge path-limitportion and the anode portion. With such a constitution, improvement inpositioning accuracy between the second discharge path-limit portion andthe anode portion can be achieved.

Moreover, it is preferable that the gas discharge tube further comprisesa third discharge path-limit portion, arranged in a midway of thedischarge path between the second discharge path-limit portion and theanode portion, and provided with a third opening for narrowing thedischarge path. The first, second and third discharge path-limitportions are electrically insulated from one another, respectively. Byproviding the third discharge path-limit portion in this manner, furtherhigh luminance is achieved. At this time, since the first, second andthird discharge path-limit portions are electrically insulated from oneanother respectively, the first, second and third discharge path-limitportions can be set to different potentials, respectively. Accordingly,by adjusting each potential, discharge at a starting time is facilitatedso as to pass through the insides of the second opening. As a result,discharge between the cathode portion and the anode portion is to bestarted rapidly, so that the starting properties of the lamp can beimproved even in case of using three discharge path-limit portions.

In addition, it is preferable that the second and third dischargepath-limit portions are shielded from the cathode portion by insulatingmaterial. With such a constitution, occurrence of an abnormal dischargedue to bending around-discharge extending from the cathode portiontoward the second and third discharge path-limit portions is prevented.

Further, it is preferable that an annular spacer of insulating materialfor positioning the third discharge path-limit portion and the anodeportion is provided between the third discharge path-limit portion andthe anode portion. With such a constitution, improvement in positioningaccuracy between the third discharge path-limit portion and the anodeportion can be achieved.

The present invention is made further sufficiently understandableaccording to the following detailed description and the attacheddrawings. These are merely shown for exemplification, and it should notbe thought that they limit the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a first embodiment of a gas dischargetube according to the present invention.

FIG. 2 is a transverse sectional view of the gas discharge tube shown inFIG. 1.

FIG. 3 is a sectional view showing a second embodiment of a gasdischarge tube according to the present invention.

FIG. 4 is a transverse sectional view of the gas discharge tube shown inFIG. 3.

FIG. 5 is a sectional view showing a third embodiment of a gas dischargetube according to the present invention.

FIG. 6 is a transverse sectional view of the gas discharge tube shown inFIG. 5.

FIG. 7 is a sectional view showing a fourth embodiment of a gasdischarge tube according to the present invention.

FIG. 8 is a transverse sectional view of the gas discharge tube shown inFIG. 7.

FIG. 9 is a sectional view showing a fifth embodiment of a gas dischargetube according to the present invention.

FIG. 10 is a transverse sectional view of the gas discharge tube shownin FIG. 9.

FIG. 11 is a sectional view showing a sixth embodiment of a gasdischarge tube according to the present invention.

FIG. 12 is a transverse sectional view of the gas discharge tube shownin FIG. 11.

FIG. 13 is a sectional view showing a seventh embodiment of a gasdischarge tube according to the present invention.

FIG. 14 is a transverse sectional view of the gas discharge tube shownin FIG. 13.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of a gas discharge tube according to the presentinvention will be explained in detail below with reference to thedrawings.

[First Embodiment]

As shown in FIG. 1 and FIG. 2, a gas discharge tube 1 is a deuteriumlamp of a side-on type, and the discharge tube 1 has a sealed container2 made of glass in which deuterium gas is enclosed in an amount of aboutseveral hundreds Pa. This sealed container 2 comprises a cylindricalside tube 3 whose one end side is sealed and a stem 5 for sealing theother end side of the side tube 3, and one portion of the side tube 3 isutilized as a light emitting window 4. Then, a light emitting assembly 6is accommodated inside the sealed container 2.

The light emitting assembly 6 has an electrically conductive casing 7made of metal such as nickel or the like, and the casing 7 is welded andfixed to a distal end of a stem pin 8 which is provided on the stem 5upstanding so as to extend in Y direction of a tube axis. Further, aplate-like anode portion 9 is accommodated inside the light emittingassembly 6, and the anode portion 9 is welded and fixed to a distal endportion of a stem pin 10 which is provided on the stem 5 upstanding soas to extend in the Y direction of the tube axis. Then, the stem pin 10is accommodated in a pipe 11 made of alumina or the like in order tomaintain an electrically insulating property inside the sealed container2.

Further, a second discharge path-limit portion 12 facing the anodeportion 9 is accommodated inside the casing 7, and the second dischargepath-limit portion 12 is welded and fixed to the casing 7 via anelectrically conductive metal-made supporting plate 15. The seconddischarge path-limit portion 12 is made of electrically conductive metal(for example, molybdenum, tungsten, or alloy made of these material) andhas a cup portion 13 for forming an arc ball, and this cup portion 13 isspread toward the light emitting window 4 so as to receive an arc ballproduced by discharge to take out light with high luminance efficiently.Further, a second opening 14 for narrowing a discharge path is providedat a bottom portion of the cup portion 13, and the second opening 14comprises, for example, a small hole with a diameter of about 0.5 to 1mm.

Furthermore, a first discharge path-limit portion 16 facing the seconddischarge path-limit portion 12 is fixed to the casing 17, and the firstdischarge path-limit portion 16 is welded and fixed to the casing 7 viaan electrically conductive metal-made supporting plate 17. The firstdischarge path-limit portion 16 is made of electrically conductive metal(for example, molybdenum, tungsten, or alloy made of these material) andhas a cup portion 18 for forming an arc ball, and this cup portion 18 isspread toward the light emitting window 4 so as to receive an arc ballproduced by discharge to take out light with high luminance efficiently.Further, a first opening 19 for narrowing the discharge path is providedat a bottom portion of the cup portion 18, and the first opening 19comprises a small hole with a diameter equal to or more than that of thesecond opening 14 (for example, about 0.5 to 1 mm). Then, the firstopening 19 and the second opening 14 are aligned on an optical axis lineX.

In the light emitting assembly 6, also, a cathode portion 20 is arrangedat a position deviated from an optical path, and the cathode portion 20has a coil portion made of tungsten for generating thermions (refer toFIG. 2). Then, one end of the cathode portion 20 is welded andelectrically connected to a stem pin 21 provided upstanding on the stem5, and the other end of the cathode portion 20 is welded andelectrically connected to a stem pin 22 provided upstanding on the stem5.

Furthermore, a discharge rectifying plate 23 is provided at a positiondeviated from the optical path between the cathode portion 20 and thefirst discharge path-limit portion 16. An electron emission opening 24for allowing passing through of thermions is formed at the dischargerectifying plate 23. Further, an electrically conductive front cover 26made of metal such as nickel or the like is fixed to the casing 7, and alight passage opening 27 aligned to the first opening 19 and the secondopening 14 on the optical axis line X is provided at the front cover 26.By accommodating the cathode portion 20 inside the front cover 26 inthis manner, sputtered substance or evaporated substance generated fromthe cathode portion 20 is prevented from adhering to the light emittingwindow 4.

Here, in case where light with a high luminance is to be created, it isinsufficient to simply make the openings 14 and 19 for narrowing adischarge path smaller. The smaller the opening portion is made, thegreater difficulty there arises in causing discharge at a time of lampstarting. Therefore, in order to improve starting properties of a lamp,there is need to generate a remarkably large potential differencebetween the cathode portion 20 and the anode portion 9. As a result, ithas been confirmed in an experiment the service life of the lamp becomesshort.

Therefore, a first discharge path-induction portion 29 is arrangedbetween the first discharge path-limit portion 16 and the seconddischarge path-limit portion 12 inside the casing 7. The dischargepath-induction portion 29 is welded and fixed to a distal end portion ofa stem pin 30, which is provided upstanding on the stem 5 to extend inthe Y direction of the tube axis. Then, the stem pin 30 is accommodatedin a pipe 31 made of alumina or the like in order to maintain anelectrically insulating property inside the sealed container 2 and canbe supplied with a predetermined voltage from the outside.

Further, a distal end portion of the discharge path-induction portion 29is conical, and its tip end is provided at a position slightly deviatedfrom a line connecting the first opening 19 and the second opening 14 soas not to block discharging. When the distal end of the dischargepath-induction portion 29 is sharpened in this manner, a density ofcharged particles can be enhanced at a tip end of the first dischargepath-induction portion 29 so that the starting properties of the lampcan be made better.

By adopting such a discharge path-induction portion 29 as describedabove, there can be produced between the cathode portion 20 and thefirst opening 19 an active starting discharge making it possible to passthrough the first opening 19 of the first discharge path-limit portion16. For this reason, discharge at a starting time is facilitated to passwithin the second opening 14. As a result, discharge between the cathodeportion 20 and the anode portion 9 is started rapidly. Therefore, inorder to achieve further enhancement of brightness, there can beaccomplished with ease a further miniaturization of the openings 14 and19, in terms of its area size, in the discharge path-limit portions,while the starting properties being kept excellent without any increasein the voltage at the time of lamp starting so much.

Next, an operation of the deuterium gas discharge tube 1 described abovewill be explained.

First, power of 10W or so is supplied from the external power source tothe cathode portion 20 via the stem pins 21 and 22 for about 20 secondsbefore discharging, so that a coil portion of the cathode portion 20 ispreheated. Thereafter, a voltage of about 160V is applied across thecathode portion 20 and the anode portion 9 from an external power sourceso that preparation for arc discharge is completed.

After the preparation has been completed, a trigger voltage of about350V is applied from the external power source to the dischargepath-induction section 29 via the stem pin 30. Thereby, dischargebetween the cathode portion 20 and the discharge path-induction portion29 is generated, which serves as a trigger so that discharge isgenerated between the cathode portion 20 and the anode portion 9. Then,once such a starting discharge occurs, arc discharge is maintainedbetween the cathode portion 20 and the anode portion 9, and arc ballsare generated near the respective first and second openings 19 and 14,which have narrowed the discharge path. Then, ultraviolet rays taken outfrom two arc balls pass through the light emitting window 4 to beemitted to the outside as light with an extremely high luminance.

[Second Embodiment]

As shown in FIG. 3 and FIG. 4, a gas discharge tube 34 is a deuteriumlamp of a side-on type. The gas discharge tube 34 is different from thefirst embodiment in that three discharge path-limit portions areprovided, and identical or similar constitution elements therein aredesignated with same reference numerals and explanation thereof will beomitted.

A third discharge path-limit portion 36 is accommodated between thesecond discharge path-limit portion 12 and the anode portion 9 in thecasing 7 of the gas discharge tube 34, and the third dischargepath-limit portion 36 is welded and fixed to the casing 7 via anelectrically conductive supporting plate 37 made of metal. The thirddischarge path-limit portion 36 is made of electrically conductive metal(for example, molybdenum, tungsten, or alloy made of these materials)and has a cup portion 38 for forming an arc ball, and this cup portion38 is spread toward the light emitting window 4 so as to receive an arcball produced by discharge to take out light efficiently.

Further, a third opening 39 for narrowing a discharge path is providedat a bottom portion of the cup portion 38, and the third opening 39comprises a small hole with a diameter equal to or less than that of thesecond opening 14 (for example, about 0.5 to 1 mm). Then, the firstopening 19, the second opening 14 and the third opening 39 are alignedon an optical axis line X. By utilizing the three discharge path-limitportions 12, 16 and 36 aligned in this manner, proper arc balls can beproduced at the respective cup portions 13, 18 and 38, so that furtherincrease in luminance can be achieved.

[Third Embodiment]

As shown in FIG. 5 and FIG. 6, a gas discharge tube 40 is a deuteriumlamp of a side-on type, and the gas discharge tube 40 is identical tothe second embodiment in that the three discharge path-limit portions12, 16 and 36 are provided, while there is a difference in such anarrangement that the second discharge path-limit portion 12 and thethird discharge path-limit portion 36 come closer to each other. As aresult of such an arrangement that the second discharge path-limitportion 12 and the third discharge path-limit portion 36 come closer toeach other at a distance of, for example, 0.1 mm to 1 mm there betweenin this manner, spreading of discharge can be suppressed at a locationof the discharge path positioned between the second opening 14 and thethird opening 39, so that the starting properties can be made better andluminance can be enhanced.

[Fourth Embodiment]

As shown in FIG. 7 and FIG. 8, a gas discharge tube 42 is a deuteriumlamp of a side-on type. The gas discharge tube 42 is different from thesecond embodiment in that two discharge path-induction portions areprovided, and identical or similar constitution portions thereof aredesignated with same reference numeral in the second embodiment andexplanation thereof will be made.

A second discharge path-induction portion 43 is arranged between thesecond discharge path-limit portion 12 and the third dischargepath-limit portion 36 inside the casing 7 of the gas discharge tube 42.The discharge path-induction portion 43 is welded and fixed to a distalend portion of a stem pin 44 which is provided upstanding on the stem 5so as to extend in the Y direction of a tube axis. Then, the stem pin 44is accommodated in a pipe 45 made of alumina or the like in order tomaintain an electrically insulating property within the sealed container2, and it can be supplied with a predetermined voltage from the outside.

Further, a distal end portion of the second discharge path-inductionportion 43 is conical, and its tip end is provided at a positionslightly deviated from a line connecting the second opening 14 and thethird opening 39 so as not to block discharge. By sharpening the distalend of the second discharge path-induction portion 43 in this manner, adensity of charged particles can be made higher at the tip end of thesecond discharge path-induction portion 43, so that the startingproperties of a lamp can be made better.

By adopting such a second discharge path-induction portion 43 asdescribed above, for example, a voltage of 350V is applied to the firstdischarge path-induction portion 29 and a voltage of 400V is applied tothe second discharge path-induction portion 43 at a starting time. As aresult, discharge is generated smoothly between the cathode portion 20and the first discharge path-induction portion 29, and subsequentlydischarge is generated smoothly between the cathode portion 20 and thesecond discharge path-induction portion 43, these discharges serving astriggers so that discharge is generated smoothly between the cathodeportion 20 and the anode portion 9. Then, once such a starting dischargeis generated, arc discharge is maintained between the cathode portion 20and the anode portion 9 and arc balls are generated near by the first,second and third openings 19, 14 and 39 respectively for narrowing thedischarge path. And, ultraviolet rays taken out from three arc ballspass through the light emitting window 4 to be emitted to the outside aslight with an extremely high luminance.

[Fifth Embodiment]

As shown in FIG. 9 and FIG. 10, a gas discharge tube 50 is a deuteriumlamp of a side-on type, and the discharge tube 50 has a sealed container52 made of glass in which deuterium gas is enclosed in an amount ofabout several hundreds Pa. This sealed container 52 comprises acylindrical side tube 53 whose one end side is sealed and a stem 55 forsealing the other end side of the side tube 53, and one portion of theside tube 53 is utilized as a light emitting window 54. Then, a lightemitting assembly 56 is accommodated inside the sealed container 52.

The light emitting assembly 56 has an electrically insulating casing 57made of ceramics, and the casing 57 comprises a first electricallyinsulating portion 57 a positioned at a front portion of the casing 57,a second electrically insulating portion 57 b positioned at a middleportion of the casing 57 and a third electrically insulating portion 57c positioned at a rear portion of the casing 57, wherein ease ofassembling is taken into account. The first electrically insulating body57 a and the second electrically insulating body 57 b are annular, andthey are provided in such a manner that they are coaxial to each otherand their axial directions extend along an X direction of an opticalaxis line. A stem pin 58 extending in a Y direction of the tube axis isprovided upstanding on the stem 55 to penetrate the third electricallyinsulating portion 57 c. Further, a plate-like anode portion 59 isclamped by the second electrically insulating portion 57 b and the thirdelectrically insulating portion 57 c, and the anode portion 59 is weldedand fixed to a distal end portion of a stem pin 60 which is providedupstanding on the stem 55 to extend in a Y direction of the tube axis.Then, the stem pin 60 is accommodated in a pipe 61 made of alumina orthe like in order to maintain an electrically insulating property withinthe sealed container 52.

Further, a second discharge path-limit portion 62 facing the anodeportion 59 is accommodated within the casing 57, and the seconddischarge path-limit portion 62 is welded and fixed to an electricallyconductive metal-made supporting plate 65. The supporting plate 65 isfixed to the casing 57 in such a way that it is interposed between thefirst electrically insulating portion 57 a and the second electricallyinsulating portion 5. In this manner, the second discharge path-limitportion 62 is positioned, being kept interposed between the firstelectrically insulating portion 57 a and the second electricallyinsulating portion 5, via the metal-made supporting plate 65. Further,the anode 59 is positioned, being kept interposed between the secondelectrically insulating portion 57 b and the third electricallyinsulating portion 57 c. Accordingly, the second electrically insulatingportion 57 b functions as a spacer for positioning the anode portion 59and the second discharge path-limit portion 62, so that positioningimprovement for these members can be achieved. The second dischargepath-limit portion 62 is made of electrically conductive metal (forexample, molybdenum, tungsten, or alloy made of these material) and hasa cup portion 63 for forming an arc ball, and this cup portion 63 isspread toward the light emitting window 4 so as to receive an arc ballproduced by discharge to take out light with a high luminanceefficiently. Further, a second opening 64 for narrowing the dischargepath is provided at a bottom portion of the cup portion 63, and thesecond opening 64 comprises, for example, a small hole with a diameterof about 0.5 to 1 mm.

In addition, since the casing 57 is constituted with an electricallyinsulating ceramics, and a first discharge path-limit portion 66 and asecond discharge path-limit portion 62 described later are electricallyinsulated from each other, the first discharge path-limit portion 66 andthe second discharge path-limit portion 62 can be set to voltagesdifferent from each other in order to enhance a starting properties ofthe lamp. Therefore, in order to apply a predetermined voltage to thesecond discharge path-limit portion 62, the metal supporting plate 65 iselectrically connected to a distal end portion of a stem pin(not shown)which is provided upstanding on the stem 55 to extend in a Y directionof a tube axis.

Furthermore, the second discharge path-limit portion 62 is accommodatedin the casing 57 constituted by the first to third electricallyinsulating portions 57 a to 57 c, and it is shielded from a cathodeportion 70 such that it can not been seen from the cathode portion 70.Thereby, thermions are prevented from traveling to the second dischargepath-limit portion 62 through a route other than a route passing througha first opening 69 of the first discharge path-limit portion 66 andoccurrence of an abnormal discharge is prevented.

Moreover, the first discharge path-limit portion 66 facing the seconddischarge path-limit portion 62 is fixed to the casing 57. The firstdischarge path-limit portion 66 is welded and fixed to an electricallyconductive metal-made supporting plate 67 arranged at a front face ofthe first electrically insulating portion 57 a, and the supporting plate67 is welded and fixed to a distal end of the stem pin 58. The firstdischarge path-limit portion 66 is made of electrically conductive metal(for example, molybdenum, tungsten, or alloy made of these material) andhas a cup portion 68 for forming an arc ball, and this cup portion 68 isspread toward the light emitting window 54 so as to receive an arc ballproduced by discharge to take out light efficiently. Further, a firstopening 69 for narrowing a discharge path is provided at a bottomportion of the cup portion 68, and the first opening 69 comprises asmall hole with a diameter equal to or more than that of the secondopening 64 (for example, about 0.5 to 1 mm). Then, the first opening 69and the second opening 64 are aligned on an optical axis line X.

Furthermore, a cathode portion 70 is arranged at a position slightlydeviated from an optical oath in the light emitting assembly 56 and thecathode portion 70 has a coil portion made of tungsten for generatingthermions (refer to FIG. 10). Then, one end of the cathode portion 70 iswelded and electrically connected to a stem pin 71 provided upstandingon the stem 55, and the other end of the cathode portion 70 iselectrically connected to a stem pin 72 provided upstanding on the stem55 via a lead portion welded to the stem pin 72.

In addition, a discharge rectifying plate 73 is provided at a positiondeviated from the optical path between the cathode portion 70 and thefirst discharge path-limit portion 66 and the discharge rectifying plate73 is formed with an electron emitting opening 74 for allowingpassing-through of thermions. Further, the casing 57 is fixed with anelectrically conductive front cover 76 made of metal such as nickel orthe like, and the front cover 76 is provided with a light passageopening 77 which is aligned to the first opening 69 and the secondopening 64 on the optical axis line X. By accommodating the cathodeportion 70 within the front cover 76 in this manner, sputter substanceor evaporated substance generated from the cathode portion 70 isprevented from adhering to a light emitting window 54.

Here, in case where light with high luminance is to be created, it isinsufficient to simply make the openings 64 and 69 for narrowing thedischarge path smaller. The smaller the openings are made, the greaterdifficulty arises in causing discharge at a time of lamp starting.Therefore, in order to improve starting properties of a lamp, there isneed to generate a remarkably large potential difference between thecathode portion 70 and the anode portion 59. As a result, it has beenconfirmed in an experiment that the service life of the lamp becomesshort.

Therefore, a first discharge path-induction portion79 is arrangedbetween the first discharge path-limit portion 66 and the seconddischarge path-limit portion 62 inside the casing 57. The dischargepath-induction portion 79 is welded and fixed to a distal end portion ofa stem pin 80, which is provided upstanding on the stem 55 to extend inthe Y direction of the tube axis. Then, the stem pin 80 is accommodatedin a pipe 81 made of alumina or the like in order to maintain anelectrically insulating property inside the sealed container 52 and canbe supplied with a predetermined voltage from the outside.

Further, a distal end portion of the discharge path-induction portion 79is conical, and its tip end is provided at a position slightly deviatedfrom a line connecting the first opening 69 and the second opening 64 soas not to block discharge. When the distal end of the dischargepath-induction portion 79 is sharpened in this manner, a density ofcharged particles can be enhanced at a tip end of the first dischargepath-induction portion 79 so that the starting properties of the lampcan be made better.

By adopting such a discharge path-induction portion 79 as describedabove, there can be produced between the cathode portion 70 and thefirst opening 69 an active starting discharge making it possible to passthrough the first opening 69 of the first discharge path-limit portion66. For this reason, discharge at a starting time is facilitated to passwithin the second opening 64. As a result, discharge between the cathodeportion 70 and the anode portion 59 is started rapidly. With such aconstitution, in order to achieve further enhancement of luminance, afurther miniaturization of the openings 64 and 69, in terms of its areasize, in the discharge path-limit portions can be accomplished easilywhile the starting properties is kept excellent without any increase inthe voltage at the time of lamp starting so much. Incidentally,reference numeral 99 denotes a stem pin for supporting the lightemitting assembly 59.

Next, an operation of the deuterium gas discharge tube 1 described abovewill be explained.

First, power of 10 W or so is supplied from the external power source tothe cathode portion 70 via the stem pins 71 and 72 for about 20 secondsbefore discharge, so that a coil portion of the cathode portion 70 ispreheated.

Thereafter, a voltage of about 160V is applied across the cathodeportion 70 and the anode portion 59 from an external power source sothat preparation for arc discharge is completed.

After the preparation has been completed, a trigger voltage of about370V is applied from the external power source to the second dischargepath restricting section 62 via a stem pin (not shown), and a triggervoltage of about 350V is similarly applied from an external power sourceto the discharge path-induction portion 29 via the stem pin 80. Thereby,discharge between the cathode portion 70 and the dischargepath-induction portion 79 is generated, which serves as a trigger sothat discharge is generated between the cathode portion 70 and the anodeportion 59. Then, once such a starting discharge occurs, arc dischargeis maintained between the cathode portion 70 and the anode portion 59,and arc balls are generated near the respective first and secondopenings 69 and 64, which have narrowed the discharge path. Then,ultraviolet rays taken out from two arc balls pass through the lightemitting window 54 to be emitted to the outside as light with anextremely high luminance.

[Sixth Embodiment]

As shown in FIG. 11 and FIG. 12, a gas discharge tube 84 is a deuteriumlamp of a side-on type. The gas discharge tube 84 is different from thefifth embodiment in that three discharge path-limit portions areprovided, and identical or similar constitution elements therein aredesignated with same reference numerals and explanation thereof will beomitted.

A third discharge path-limit portion 86 is accommodated between thesecond discharge path-limit portion 62 and the anode portion 59 in thecasing 57 of the discharge tube 84, and the third discharge path-limitportion 86 is welded and fixed to an electrically conductive metal-madesupporting plate 87. The supporting plate 87 is fixed to the casing 57being interposed between the second electrically insulating portion 57 band a fourth electrically insulating portion 57 d. The fourthelectrically insulating body 57 d is annular, and it is providedcoaxially with the first electrically insulating body 57 a and thesecond electrically insulating body 57 b. Thus, the third dischargepath-limit portion 86 is positioned, being kept interposed between thesecond electrically insulating portion 57 b and the fourth electricallyinsulating portion 57 d, via the metal-made supporting plate 87.Further, the anode portion 59 is positioned, being kept interposedbetween the fourth electrically insulating portion 57 d and the thirdelectrically insulating portion 57 c. Accordingly, the fourthelectrically insulating portion 57 d functions as a spacer forpositioning the anode portion 59 and the third discharge path-limitportion 86, so that positioning accuracy for these members can beachieved. The third discharge path-limit portion 86 is made ofelectrically conductive metal (for example, molybdenum, tungsten, oralloy made of these material) and has a cup portion 88 for forming anarc ball, and this cup portion 88 is spread toward the light emittingwindow 54 so as to receive an arc ball produced by discharge to take outlight efficiently.

Further, a third opening 89 for narrowing a discharge path is providedat a bottom portion of the cup portion 88, and the third opening 89comprises a small hole with a diameter equal to or less than that of thesecond opening 64 (for example, about 0.5 to 1 mm). Then, the firstopening 69, the second opening 64 and the third opening 89 are alignedon an optical axis line X. By utilizing the three discharge path-limitportions 62, 66 and 86 aligned in this manner, proper arc balls can beproduced at the respective cup portions 63, 68 and 88, so that furtherincrease in luminance can be achieved.

Then, as a result of such an arrangement that the second dischargepath-limit portion 62 and the third discharge path-limit portion 86 comecloser to each other, spreading of discharge can be suppressed at alocation of the discharge path positioned between the second opening 64and the third opening 89, so that a starting properties can be madebetter and luminance can be enhanced.

Further, since the casing 57 is constituted with electrically insulatingceramics, and a first discharge path-limit portion 66, a seconddischarge path-limit portion 62 and a third discharge path-limit portion86 are electrically insulated from one another, the first dischargepath-limit portion 66, the second discharge path-limit portion 62 andthe third discharge path-limit portion 86 may be set to differentvoltages, so that the starting properties of the lamp can be enhanced.

Furthermore, the second and third discharge path-limit portions 62 and86 are accommodated in the casing 57 constituted by with the first tofourth electrically insulating portions 57 a to 57 d, so that they areshielded from the cathode portion 70 such that they can not be seen fromthe cathode portion 70. Thereby, thermions are prevented from travelingto the second and third discharge path-limit portions 62 and 86 througha route other than a route passing through the first opening 69 of thefirst discharge path-limit portion 66, and occurrence of abnormaldischarge is prevented.

[Seventh Embodiment]

As shown in FIG. 13 and FIG. 14, a gas discharge tube 92 is a deuteriumlamp of a side-on type. The gas discharge tube 92 is different from thesixth embodiment in that two discharge path-induction portions areprovided, and identical or similar constitution elements therein aredesignated with same reference numerals and explanation thereof will beomitted.

A second discharge path-induction portion 93 is arranged between thesecond discharge path-limit portion 62 and the third dischargepath-limit portion 86 in a casing 57 of the gas discharge tube 92. Thedischarge path-induction portion 93 is welded and fixed to a distal endportion of a stem pin 94, which is provided upstanding on the stem 55 soas to extend in the Y direction of a tube axis. Then, the stem pin 94 isaccommodated in a pipe 95 made of alumina or the like in order tomaintain an electrically insulating property within the sealed container52, and it can be supplied with a predetermined voltage from theoutside.

Further, a distal end portion of the second discharge path-inductionportion 93 is conical, and its tip end is provided at a positionslightly deviated from a line connecting the second opening 64 and thethird opening 89 so as not to block discharge. By sharpening the distalend of the second discharge path-induction portion 93 in this manner, adensity of charged particles can be made higher at the tip end of thesecond discharge path-induction portion 93, so that the startingproperties of a lamp can be made better.

By adopting the second discharge path-induction portion 93 as describedabove, for example, a voltage of 350V is applied to the first dischargepath-induction portion 79 and a voltage of 400V is applied to the seconddischarge path-induction portion 93 at a starting time. As a result,discharge is generated smoothly between the cathode portion 70 and thefirst discharge path-induction portion 79, and subsequently discharge isgenerated smoothly between the cathode portion 70 and the seconddischarge path-induction portion 93, these discharges serving astriggers so that discharge is generated smoothly between the cathodeportion 70 and the anode portion 59. Then, once such a startingdischarge is generated, arc discharge is maintained between the cathodeportion 70 and the anode portion 59 and arc balls are generated near bythe respective first, second and third openings 69, 64 and 89 fornarrowing the discharge path. And, ultraviolet rays taken out from threearc balls pass through the light emitting window 54 to be emitted to theoutside as light with an extremely high luminance.

Incidentally, in the gas discharge tubes 50 and 84 according to thefifth and sixth embodiments described above, such a constitution isemployed that the first discharge path-induction portion 79 is provided,but a gas discharge tube can be constituted without providing such adischarge path-induction portion 79. Further, in the gas discharge tube92 according to the seventh embodiment, such a constitution is employedthat the first and second discharge path-induction portions 79 and 93are provided, but a gas discharge tube can be constituted withoutproviding such discharge path-induction portions 79 and 93.

From the above explanation of the present invention, it will be apparentthat the present invention can be modified variously. It cannot berecognized that such a modification is deviated from the spirit andscope of the present invention, and all improvements obvious for thoseskilled in the art are included in the scope of claims described below.

Industrial Applicability

According to the present invention, a gas discharge tube whose startingproperties is excellent while realizing high luminance can be provided.

1. A gas discharge tube for emitting a predetermined light from a lightemitting window of a sealed container with a charged gas toward theoutside by producing a discharge between a cathode portion and an anodeportion enclosed in said container, said tube comprising: a firstdischarge path-limit portion, arranged in a midway of a discharge pathbetween said anode portion and said cathode portion, and provided with afirst opening for narrowing said discharge path; a second dischargepath-limit portion, arranged in a midway of the discharge path betweensaid first discharge path-limit portion and said anode portion, andprovided with a second opening for narrowing said discharge path; and afirst discharge path-induction portion, arranged between said firstdischarge path-limit portion and said second discharge path-limitportion, and electrically connected to an external power source.
 2. Agas discharge tube according to claim 1, wherein said first dischargepath-limit portion and said second discharge-path-limit portion areelectrically insulated from each other.
 3. A gas discharge tubeaccording to claim 1, wherein a distal end portion of said firstdischarge path-induction portion is conical.
 4. A discharge tubeaccording to claim 1, wherein the first and second openings of saidfirst and second discharge path-limit portions are formed at bottomportions of cup portions spread toward said light emitting window.
 5. Agas discharge tube according to claim 1, further comprising a thirddischarge path-limit portion, arranged in a midway of said dischargepath between said second discharge path-limit portion and said anodeportion, and provided with a third opening for narrowing said dischargepath.
 6. A gas discharge tube according to claim 5, wherein said seconddischarge path-limit portion and said third discharge path-limit portionare electrically insulated from each other.
 7. A gas discharge tubeaccording to claim 5 wherein the third opening of said third dischargepath limit portion is formed at a bottom portion of a cup portion spreadtoward said light emitting window.
 8. A gas discharge tube according toclaim 5, comprising a second discharge path-induction portion, arrangedbetween said second discharge path-limit portion and said thirddischarge path-limit portion, and electrically connected to an externalpower source.
 9. A gas discharge tube according to claim 8, wherein adistal end portion of said second discharge path-induction portion isconical.
 10. A gas discharge tube according to wherein said seconddischarge path-induction portion is applied to a voltage higher thanthat applied to said first discharge path-induction portion.
 11. A gasdischarge tube for emitting a predetermined light from a light emittingwindow of a sealed container with a charged gas toward the outside byproducing a discharge between a cathode portion and an anode portionenclosed in said container, said tube comprising: a first dischargepath-limit portion, arranged in a midway of a discharge path betweensaid anode portion and said cathode portion, and provided with a firstopening for narrowing said discharge path; and a second dischargepath-limit portion, arranged in a midway of the discharge path betweensaid first discharge path-limit portion and said anode portion, andprovided with a second opening for narrowing said discharge path; saidfirst discharge path-limit portion and said second discharge path-limitportion being electrically insulated from each other.
 12. A gasdischarge tube according to claim 11, wherein said second dischargepath-limit portion is shielded from said cathode portion by insulatingmaterial.
 13. A gas discharge tube according to claim 12, wherein anannular spacer of insulating material for positioning the seconddischarge path-limit portion and the anode portion is provided betweensaid second discharge path-limit portion and said anode portion.
 14. Agas discharge tube according to claim 11, further comprising a thirddischarge path-limit portion, arranged in a midway of said dischargepath between said second discharge path-limit portion and said anodeportions, and provided with a third opening for narrowing said dischargepath, said first, second and third discharge path-limit portions beingelectrically insulated, respectively.
 15. A gas discharge tube accordingto claim 14, wherein said second and third discharge path-limit portionsare shielded from said cathode portion by insulating material.
 16. A gasdischarge tube according to claim 15, wherein an annular spacer ofinsulating material for positioning the third discharge path-limitportion and the anode portion is provided between said third dischargepath-limit portion and said anode portion.